This just started happening. The message "Low Coolant Level" flashes on the display intermittently, but the level in the tank is actually OK (thank goodness).

I searched around and good 'ol Merlin had a similar problem a few years ago:
https://www.freel2.com/forum/post319158.html#319158

I will try jiggling a few things before I replace the expansion tank (LR004080).

 

The connector might have also come loose.

 

That's what I was hoping, so I removed it, inspected for corrosion, and reseated the connector. I also attempted to jiggle the internal float, but I doubt I was successful as there is a plastic cap that blocks direct access through the cap opening.

The warning message came back on today after staying off for a day or so. The coolant level is still OK, so clearly a measurement problem.

The float is internal to the tank, so the float and tank are purchased together (LR004080). The sensor which attaches to the bottom of the tank is a separate part (LR000930).

I don't know for certain if the problem is the float or the sensor, so I will probably replace both. Amazon has an inexpensive bundle for the tank, sensor, and even a new cap. Sounds great but the brand is KARPAL which I never heard of. May as well be "PARTS4U".

Another aftermarket part on Amazon which has some brand recognition is REIN. They offer the same bundle for a higher price, but still a lot less than genuine OEM so I might go with them.

I was planning to do a drain/fill of the radiator coolant anyway, so I will swap this out at the same time.

 

It's probably got 13 years of crud stuck somewhere in there. Not worth trying to fix it when replacements are so inexpensive.

 

It's almost certainly the float, they lose their buoyancy over time. Probably just need a new tank & float every ten years or so.

I wouldn't waste money on replacing the sensor separately, the replacement tanks I've seen actually come with a new sensor anyway.

This one worked fine for me, it is the Karpal:

 

I replaced the coolant tank this weekend following the helpful instructions Merlin provided on the other forum (link in first post above). Additionally, here are a few of my own comments:

> There is an outlet tube on the bottom of the tank with a black cap over it. I thought it would be a simple matter to slip a hose over it and let the tank drain. But none of the fluid came out. It was puzzling so I just moved on and poured out the coolant from the other openings. Thinking about it afterwards, it might have required a forced punch to make a hole to drain the tank. It might be intended when you are replacing the tank and don't really care that you're making a hole in the bottom. Just speculating, and if I were to replace it again that's what I would try first.

> Before replacing the tank, while you have the new one in your hands, it's a good time to use a Sharpie and draw a line over the Max/Min fill lines so they are easier to see when checking the level.

> Have an assortment of rubber plugs handy for the hoses as you remove them from the tank.

> Once installed, refill the new tank to less than the Min line to test that the low level indicator actually works (as Merlin suggested). After confirming the float and sensor work, you can top it off to the normal level. One thing I noticed is that the low level indicator with the new tank comes on when the level is about 3/4" below the Min line. On the original tank, the low level indicator came on sooner, about 1/8" below the Min line. So I will be prompt about attending to this indicator if it comes on again as the level will be significantly below the Min line.

While the hood was up and I felt ambitious, I also changed the oil & filter. I had already repositioned the Power Steering and Windshield Wiper Fluid reservoirs to replace the coolant tank, and I discovered that the oil filter comes out and goes in MUCH more easily with the Windshield Wiper Fluid reservoir neck unbolted and shifted to the left. I had always lifted/moved the Power Steering bottle to the right, but I never took the extra minute to remove the 10mm bolt that holds the Windshield Wiper fluid neck. That's serendipity!